Removal of contaminant particles from forced air heating/cooling systems is conventionally accomplished by a filter placed between a duct carrying air back to the heating/cooling system and the fan used to propel the air. However, these filters do not remove contaminant particles located between the heating/cooling system and the forced air duct outlet. For example, dust accumulates within the duct work extending between the heating/cooling system and the register covering a forced air duct outlet. In order to capture the dust and contaminant particles existing between the heating/cooling system and the air duct outlet, filter units have been positioned within a register which covers the forced air duct outlet. U.S. Pat. No. 5,240,487 to Kung discloses such a filter unit. The Kung '487 patent discloses a frame which supports an air filter wherein the frame is inserted into a forced air heating and/or cooling system duct adjacent to a duct outlet and within a floor or wall register. Specifically, the frame and air filter is friction fitted within the skirt of the register. The air filter comprises a two-ply fibrous sheet with an opening between the plies to receive the frame. A scent dispenser is mounted to the frame for containing scented air freshening material. The frame and filter unit of the Kung '487 patent has a number of disadvantages. The frame and filter unit requires complicated manufacturing methods and therefore is costly to manufacture. Also, the frame and air filter unit is a complicated structural arrangement for accomplishing a simple task. It is desirable to produce a register filter assembly having a simple structural arrangement which is easy to manufacture.